1. Field of the Invention
This invention relates to concrete control joints, and in particular, to a structurally integral hinged control joint.
2. Description of the Prior Art
Areas of poured concrete, as highway sections or airport runway sections, have been observed to experience cracking along unpredictably locatable planes. Such cracking may occur in response to tensil forces imposed at opposite ends of the slab as, for example, at the connection therewith to the next-adjacent concrete slab.
In order to limit, or at least render predictable the locations at which cracking occurs, it is common practice in the art to artificially introduce weakened areas within the concrete slab, so that cracking which would occur would be expected along the weakened planes. For example, it is known to provide across the transverse dimension of the concrete slab at predetermined locations thereon a number of cuts extending into the concrete several inches, each cut being the width of one rotary saw blade, or approximately one-eighth of an inch. The cuts are usually displaced in some predetermined pattern in the concrete slab and any cracking of the concrete maybe expected along planes emanating from the cut.
It is also a common practice in the art to introduce substantially T-shaped plastic members transversally across a slab of concrete with the upright leg of the T extending into the concrete and the arms disposed along the surface thereof. The upright leg of the T may be viewed as a weakened plane joint and concrete cracking or fracturing may be expected to occur along that weakened plane joint.
However, in the case of either prior art expedient, once the crack occured moisture is permitted to enter through the crack into the body of the concrete slab. In the case of the saw blade cut, water accumulates in the volume defined by the cut and falls by gravity into the fissures or cracks emanating therefrom. With the case of the T-shaped plastic members, moisture seeps under the extending arms of the T-shaped member along the sides of the upright leg thereof, and into the fracture extending from the lower end of the leg. The presence of moisture within the fissures within the body of the concrete erodes the concrete, and, dependent upon climatic conditions, may expand or contract in accordance with the temperature to accelerate the deterioration of the concrete body.
It would therefore be advantageous to provide a concrete control joint fabricated of a metal material in a unitized construction such that moisture and the like is prevented from entering cracks within the concrete body emanating from the control joint. It is of further advantage to provide an integrally fabricated control joint of a hinged construction such that the hinge acts as a water stop to prohibit entry of water into the fissures generated within the concrete. It would be of yet further advantage to provide a control joint having fingers or the like adaptable to engage the edges of the concrete to secure the arms of the control joint thereto to thereby protect those edges from deterioration and erosion.